THE YELLOWSTONE HOTSPOT TRACK—INTEGRATED PARAMETERS FAVOR MODEL OF A DEEP-SEATED PLUME HEAD FOLLOWED BY A PLUME TAIL

The nature of large-scale processes driving the Yellowstone hotspot is reflected in its surface geologic record, geophysical expression, and analog to other hotspots. Recent tomographic images reveal a plume-like feature extending from Yellowstone to ~500-600 km depth and inclined 70° NW. The Yellowstone geoid anomaly, an 800-km-wide topographic swell centered on Yellowstone, is the largest geoid anomaly in the conterminous US.

The hotspot's track began ~ 16 Ma with eruption of flood basalts in Oregon and Washington and extensive rhyolite volcanism and mafic dikes in Nevada and Oregon over a N-S distance of ~1,000 km. A large-diameter plume head (Draper, 1991; Camp, 1995; Pierce et al., 2002) may explain the widespread volcanism and intrusions. Basaltic magma from decompression melting of rising mantle resulted in flood basalts erupted through thin, young oceanic crust, whereas in sialic crust, basaltic magma melted the crust to produce rhyolites.

The track's smaller diameter plume tail was underway by 10 Ma. Since then, a systematic progression of volcanism, faulting, and uplift has advanced NNE to Yellowstone at the same rate (25 km/m.y) and in the opposite direction as the North American plate. The Yellowstone crescent of high terrain (YCHT) has a “bow-wave” configuration that is characterized by uplift in advance of volcanism. Belts of gravity-driven fault activity on the inner slope of the YCHT accompany volcanism. Both the YCHT and belts of faulting flare out more (1.6 x wider) on the south side of the track, possibly related to the SE rise of the plume.

Seismic tomography images the plume into the mantle transition zone at 500-600 km depth but “… lower mantle plumes may be so altered by the transition zone that they appear to originate from within it.” (Schubert et al., 2001). The ~ 1,000 km N-S geologic manifestations of the starting plume suggest inflation of the inferred plume-head was sourced from deeper than 500 km, as may the present 800-km-wide geoid anomaly. The plume head is centered in the Basin and Range province; its 16 Ma arrival correlates with changes in tectonics and volcanism (Pierce et al., 2002). Parsons et al. (1994) postulated spreading of the plume head beneath the Basin and Range/Sierras; perhaps such spreading is responsible for the inferred displacement of the lithospheric root of the Sierra Nevada.